Identification

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Satellites

The CLUSTER mission comprises four satellites with identical instruments onboard. Once placed on a near-polar, highly elliptical orbit (4 to 19.6 Earth radii from the perigee to the apogee), they fly in formation occupying the apexes of a tetrahedron of variable dimensions.

Each satellite weighs 1,200 kg of which more than half is composed of propellants used for positioning and formation flight control. It has a cylindrical shape 2.9 m in diameter and 1.3 m high.

Satellites are spin stabilized with the spin axis perpendicular to the ecliptic, spin rate is 15 rpm.

Power is supplied by solar cells around the edge of the satellite (224 Watts end of life). The payload includes 11 instruments designed to measure the magnetic field, waves and particles.

Measurement of the direct magnetic field by means of:

FGM: Flux Gate Magnetometer

An active electric field measuring experiment using electron beam drift:

EDI: Electron Drift Instrument

Five instruments to measure waves. To obtain maximum scientific feedback from the resources available on the four spacecrafts, wave specialist experimenters founded the Wave Experiment Consortium (WEC), which manages the five "waves" experiments designed to measure electrical and magnetic fluctuations inside the critical layers of the Earth's magnetosphere. The five instruments are:

EFW: Electrical Field and Wave

DWP: Digital Wave Processing

STAFF: Spatio-Temporal Analysis of Field Fluctuations

WHISPER: Waves of HIgh frequency and Sounder for Probing the Electron density by Relaxation

WBD: WideBand Data

Electrical measurements (direct field and waves) are taken using four 50-meter-long antennas. France is building the WEC assembly power supply converter, is the prime contractor for STAFF and WHISPER instruments and is the technical co-ordinator for the five Waves experiments.

Three instruments for particle measurement

CIS: Cluster Ion Spectrometry

PEACE: Plasma Electron And Current AnalysEr

RAPID: Research with Adaptive Particle Imaging Detectors

France is the prime contractor for the CIS experiment devoted to ion analysis, and is also taking part in the PEACE experiment, under British prime contractorship, devoted to electron analysis. RAPID measures higher energy particles.

A satellite potential control experiment by ion emission

ASPOC: Active Spacecraft POtential Control

The payload weighs 72 kg and consumes 47 watts. Part of this payload makes use of two booms 4.5 m long to keep the magnetic field measurement experiment away from the body of the satellite and thereby reduce perturbations.

The four satellites were launched in pairs on two russian Soyuz vehicles (via STARSEM), from Baikonour in July and August 2000.